柴达木地块北缘牛鼻子梁铜镍硫化物矿床地质特征及成因

牛鼻子梁岩体位于柴达木地块北缘俄博梁断隆区,是一个出露面积约8 km²的镁铁质—超镁铁质层状杂岩体,呈岩床状,东西向延长; 堆晶结构与堆晶层理发育,可划分出多个堆晶韵律与旋回,岩石类型丰富,具有橄榄岩相、辉石岩相和辉长岩相等多种岩石类型。中酸性端元的岩石类型有石英闪长岩和英云闪长岩,证明岩浆经历了以分离结晶为主导性机制的分异演化过程。岩浆富水,结晶出大量褐色普通角闪石,形成角闪石岩。岩体中含有大量的古元古界金水口岩群捕虏体,同化混染严重。该岩体内含有2层层状矿体,一层在海拔3 100 m处,另一层在海拔2 800～2 900 m处。此外,在岩体西端还有一个被断层活化迁移后赋存在断层带中的热液型矿体。矿石构造主要呈浸染状、海绵陨铁状和块状; 成矿过程可划分为3个成矿期(岩浆期、矿浆期和岩浆热液期)和4个成矿阶段。结果表明:岩浆自身的分异演化与同化混染作用共同导致了硫化物熔离; 成矿过程具有明显的多期多阶段性,而非连续过程。

Geological Feature and Genesis of Niubiziliang Cu-Ni Sulphide Deposit in the Northern Margin of Qaidam Block

Niubiziliang Intrusion, which is located at Eboliang Fault-uplift in the northern margin of Qaidam Block, is a mafic-ultramafic bedded complex with an outcrop area of about 8 km² in shape of sill with east-west extension; cumulate texture and cumulate layer developed, and the intrusion was divided into multiple cumulate rhythms and cycles; rock types were abundant and included peridotite phase, pyroxenite phase, gabbro phase, etc.; rock types of intermediate-acid end-member included quartz diorite and tonalite, so that magma underwent fractional crystallization which was the dominant mechanism of differentiation and evolution process. Magma was rich in water, so that a lot of brown hornblendes were crystallized, and hornblendite was formed. The rock body contained a large number of xenoliths in Jinshuikou Terrane of Paleoproterozoic, and the assimilation-contamination was serious. The intrusion included two layered ore bodies, and the altitudes of them were 3 100 m and 2 800-2 900 m, respectively. In addition, at the western end of rock body, there was a hydrothermal ore body in the fault zone which had been migrated and activated by faults. The structures of ore mainly included disseminated, sponge iron meteorite and massive; mineralization process could be divided into three periods(magmatic period, slurry period and magmatic hydrothermal period)and four stages. The results showed that magmatic differentiation evolution and assimilation-contamination jointly led to sulfide liquation; mineralization process was multi-phase and multi-stage rather than continuous.